The present invention relates to a method and a device for preparing a medical liquid.
The invention has an application in particular in the treatment of renal insufficiency, where it can be used for preparing a dialysis liquid. In this context, the invention is particularly suitable for treating patients whose internal medium presents an excess of potassium.
The kidneys perform many functions, including elimination of water, excretion of catabolites (or waste products of metabolism, such as urea and creatinine), regulation of the concentration of electrolytes in the blood (sodium, potassium, magnesium, calcium, bicarbonates, phosphates, chlorides), and regulation of the acid-base balance of the internal medium, which balance is obtained in particular through the elimination of weak acids (phosphates, monosodium acids) and through the production of ammonium salts.
In persons who have lost the use of their kidneys, since these excretory and regulatory mechanisms no longer function, the internal medium becomes charged with water and waste products of metabolism and presents an excess of electrolytes (sodium in particular), and, in general, acidosis, with the pH of the blood plasma shifting towards 7.
To remedy kidney dysfunction, the conventional practice is to treat the blood by extracorporeal circulation in a semipermeable membrane exchanger (hemodialyzer), with circulation, on either side of the membrane, of the patient""s blood and of a dialysis liquid comprising the main electrolytes of the blood (chlorides, bicarbonates, sodium, calcium, potassium, magnesium) in concentrations close to those of the blood of a healthy subject. As a result of the physical phenomenon called dialysis, the molecules migrate from the liquid in which their concentration is highest to the liquid in which their concentration is lowest.
A significant electrolytic change in uremic patients is the increase in the potassium concentration of the plasma. Now, hyperkalemia (too high a concentration of potassium) is associated with incidents linked to hyperpolarization of the membrane of the neuromuscular cells, which can result in hypokinetic arrhythmia and complete atrioventricular block. One of the objectives of dialysis treatment is therefore to eliminate the excess potassium accumulated by the patients between two treatment sessions. In accordance with the physical principle cited above, the quantity of potassium eliminated during treatment depends directly on the difference between the concentration of the potassium in the plasma and the concentration of the potassium in the dialysis liquid, which is generally fixed at a constant level, less (approximately 2 mEq/l) than the physiological level (approximately 3.5 mEq/l).
At the start of conventional dialysis treatment, a patient with hyperkalemia (whose plasma potassium concentration can be as high as 10 mEq/l) is exposed to the undesirable effects resulting from the considerable difference between the potassium concentration of his plasma and that of the dialysis liquid: this increased gradient in fact causes a substantial diffusive flow of potassium across the membrane of the hemodialyzer, which in turn causes a substantial flow of potassium across the membrane of the cells, which affects the electric potential of the membrane at rest and, consequently, the cellular excitability. As this mechanism also influences the cardiac pacemaker cells, the patent runs the risk of cardiac arrhythmia during the dialysis treatment. This phenomenon is naturally heightened in cases of cardiac weakness and can lead to a reduction in the ejection volume affecting the cardiovascular circulation.
A particular object of the invention is therefore to modify the conditions of conventional dialysis treatment, without however affecting its effectiveness, in such a way that patients with hyperkalemia are no longer exposed to the risks mentioned above.
A general object of the invention is to conceive a device and a method for preparing a treatment liquid which can be used for extracorporeal treatment of blood, and by means of which the concentration of two ionic substances can be adjusted separately, in particular sodium and potassium (or calcium, or magnesium).
According to the invention, this object is achieved by means of a method for preparing a medical liquid from a liquid, such as water, and two concentrated solutions, comprising the following steps:
circulating the liquid in a conduit, at a flowrate Q0;
injecting into the conduit, at a flowrate Q1, a first concentrated solution containing a first ionic substance A and a second ionic substance B, the ionic substances A and B having, respectively, in the first concentrated solution, a concentration [Asol] and a first concentration [B1sol];
injecting into the conduit, at a flowrate Q2, a second concentrated solution containing the first ionic substance A and the second ionic substance B, the first ionic substance A having, in the second concentrated solution, the same concentration [Asol] as in the first concentrated solution, and the second ionic substance B having, in the second concentrated solution, a second concentration [B2sol] different than the first concentration [B1sol] in the first concentrated solution;
regulating the injection flowrate Q1 and the injection flowrate Q2 of the first and second concentrated solutions in such a way that at any given time the diluted solution resulting from the mixing of the liquid and the concentrated solutions has a desired concentration [Ades] of first substance A and a desired concentration [Bdes] of second substance B.
According to one characteristic of the invention, the injection flowrate Q1 and the injection flowrate Q2 of the concentrated solutions A and B are varied over the course of time in such a way that the concentration of the second substance B in the diluted solution varies over the course of time in accordance with a predetermined profile.
According to another characteristic of the invention, the flowrate Q0 of the liquid in the conduit is constant, and the sum of the injection flowrates Q1+Q2 of the concentrated solutions A and B is maintained constant in such a way that the concentration of the first substance A in the diluted solution remains substantially constant.
According to yet another characteristic of the invention, the injection flowrate Q1 and the injection flowrate Q2 of the concentrated solutions A and B are varied over the course of time in such a way that the concentration of the first substance A in the diluted solution varies over the course of time in accordance with a predetermined profile.
The invention also relates to a device for preparing a treatment liquid from a liquid, such as water, and two concentrated solutions, comprising:
a conduit with a first end intended to be connected to a source of liquid, such as water, and a second end for delivering a treatment liquid;
first injection means for injecting into the conduit, at a flowrate Q1, a first concentrated solution containing a first ionic substance A and a second ionic substance B, the ionic substances A and B having, respectively, in the first concentrated solution, a concentration [Asol] and a first concentration [B1sol];
second injection means for injecting into the conduit, at a flowrate Q2, a second concentrated solution containing the first ionic substance A and the second ionic substance B, the first ionic substance A having, in the second concentrated solution, the same concentration [Asol] as in the first concentrated solution, and the second ionic substance B having, in the second concentrated solution, a second concentration [B2sol] different than the first concentration [B1sol] in the first concentrated solution;
regulating means for regulating the first and second injection means and for adjusting the injection flowrate Q1 and the injection flowrate Q2 of the first and second concentrated solutions in such a way that at any given time the diluted solution resulting from the mixing of the liquid and the concentrated solutions has a desired concentration [Ades] of first substance A and a desired concentration [Bdes] of second substance B.
In one embodiment of the invention, the device for preparing treatment liquid is incorporated in a hemodialysis system, the substance A is sodium and the substance B is potassium, calcium, or magnesium. As the sodium concentration in a dialysis liquid is much higher than the potassium (calcium or magnesium) concentration, the potassium concentration can be very precisely regulated by measuring the conductivity of the mixture forming in the conduit immediately downstream of the site of injection of the first concentrated solution into the conduit, and of the mixture forming in the conduit immediately downstream of the site of injection of the second concentrated solution into the conduit (there is an excellent correlation between the conductivity of a solution and its sodium concentration).
Moreover, there is no danger of influencing the plasma potassium or calcium concentration of a patient using a very dilute dialysis solution prepared and administered by a system equipped with reliable means for measuring concentrations, which would not be the case if this objective were achieved by injection of more concentrated solution.
The invention also relates to a kit of solutions for extracorporeal treatment of blood, comprising two concentrated solutions and a bag with two compartments intended to contain each of the solutions from the kit. Each of the solutions contains at least two ionic substances A and B, the ionic substance A having the same concentration in the two solutions and the ionic substance B having different concentrations in two solutions.
According to one characteristic of the invention, the two solutions are identical except for one ionic substance whose concentration differs from one solution to the other.